https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114100
Bug ID: 114100 Summary: [avr] Inefficient indirect addressing on Reduced Tiny Product: gcc Version: 13.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: gjl at gcc dot gnu.org Target Milestone: --- The Reduced Tiny core does not support indirect addressing with offset, which basically means that every indirect memory access with a size of more than one byte is effectively POST_INC or PRE_DEC. The lack of that addressing mode is currently handled by pretending to support it, and then let the insn printers add and subtract again offsets as needed on the fly. For example, the following C code int vars[10]; void inc_var2 (void) { ++vars[2]; } is compiled to: ldi r30,lo8(vars) ; 14 [c=4 l=2] *movhi/4 ldi r31,hi8(vars) subi r30,lo8(-(4)) ; 15 [c=8 l=6] *movhi/2 sbci r31,hi8(-(4)) ld r20,Z+ ld r21,Z subi r30,lo8((4+1)) sbci r31,hi8((4+1)) subi r20,-1 ; 16 [c=4 l=2] *addhi3_clobber/1 sbci r21,-1 subi r30,lo8(-(4+1)) ; 17 [c=4 l=4] *movhi/3 sbci r31,hi8(-(4+1)) st Z,r21 st -Z,r20 where the code could be: ldi r30,lo8(vars+4) ; 28 [c=4 l=2] *movhi/4 ldi r31,hi8(vars+4) ld r20,Z+ ; 17 [c=8 l=2] *movhi/2 ld r21,Z+ subi r20,-1 ; 19 [c=4 l=2] *addhi3_clobber/1 sbci r21,-1 st -Z,r21 ; 30 [c=4 l=2] *movhi/3 st -Z,r20